Hi, I recently acquired a TFM-45 from a friend who said one channel was not working.

With no input, and power applied, both channels ping their meters, and there is a loud hum from the transformer. When I say ping the meters - the meters go full scale and back to zero or 1/2 and back up, and so on and so on. Looks like oscillation.

Is there something obvious to check or will this take a major effort to fix? service manual anywhere? I am an ex- EE and can probe everything, can bring it up with a variac, can take some oscilloscope screens if you would like.

I tried it with inputs grounded, same thing as with open circ. I then tried it with a signal on the inputs at very very low volume, same result. all this with no load on speaker terminals.

Could be the damping adjustment is way off. I know I got a loud hum when I adj mine s.t. the output volts at speaker terminals with 8 ohm load was way above spec value of 1.0 volts. It drifts (if "drift fix" service bulletin fix not done. I did this to my 45 and it no drift no mo!).Go to the "other site" (www.thecarversite.com) to get an easy download of the 45's service manual. Can find specific instructions for all this on a TFM-45 related thread here (including instructions on how to download the "virtual testbench" signal generator required to do the damping adjustment). Search my posts (elgrau) for TFM-45 key word. Do the three adjustments spelled out there and see if problem goes away. If not then probably time for a $179 "refurb" trip to "Bob's place" in Washington state!